Generally, a jib or similar is maintained between the deck (tack on the deck) and the top of the most (head) via a stay on which it is mounted (stayed).
In order to reduce the surface of the sails and adapt it to the force of the wind, it is usual to reef the main sail and to change the jibs (front sails set on the forestay) which requires time-consuming and difficult operations.
In order to overcome these drawbacks, it has been proposed to reduce the surface of the sail by taking it up progressively around its foot (rolling boom) or its luff (rolling jib).
For rolling up a jib around its luff so as to modify its surface, use is made of an apparatus known under the name of "jib roller".
In its simplest and oldest form which has been diagrammatically shown in the accompanying FIG. 1, the jib roller is provided at its base with a drum 1 fixed to the tack 2 on the deck by means of a swivel E1 and to the head of the mast 3 by means of a second swivel E2 between which the luff of the jib 5 is hoisted. When pulling the cable 6 of the roller drum 1, the jib 5 rolls up progressively about its luff 4. In a more improved device, the drum 1 and the upper swivel E2 are connected by a rotating stay on which the jib is set (made integral with) with snap hooks.
In more recent systems, the rotating stay is provided with one or two grooves in which the bolt rope of the sail can slide. These grooves can be integral with the rotating stay or can be added by means of a metal or plastic sleeves.
With these groove systems, the jib can be easily removed when not in use.
Various solutions are presently used for hoisting the jib along the rotating stay while leaving to the stay the possibility of being driven in rotation when it is desired to modify the surface of the sail by rolling it up along its luff, when the luff is made integral with the stay.
In an embodiment which is acceptable for small ships but which is inadequate for the hoisting forces required for setting the large size jibs, it is merely sufficient to use a halyard passing on a block placed below the swivel E2 at the top of the rotating stay, the extremity of the halyard, after having hoisted the jib, being fixed to the roller drum integral with the rotating stay.
On large ships however, and as diagrammatically shown in FIG. 2, for hoisting the jib 5, use is generally made of the usual halyards 7 of the ship passing on a block 8 at the top of the mast, the halyards being operated by means of a winch 9 placed at the foot of the mast.
Consequently, in this system, since the halyard 7 is fixed, it must necessarily be connected to the head of the jib by means of a swivel block E3, in order that it does not roll up about the stay. If this embodiment is satisfactory and makes it possible to ensure a good hoisting of the sail while leaving the possibility to reduce the surface thereof by rolling it up about its luff, it requires the use of three swivel devices which must have very high mechanical features since they must support the stress of the front stay, which stress may reach several tons or at least the stress of the luff which, although it is not as high, can nevertheless reach several hundreds of deca-Newtons (dN).
Consequently, in order to operate correctly, these swivels must be fitted with ball bearings, the leaktightness of which remain precarious on the bow of a ship exposed to the splashing of salt water and which very often clog up with the result that the roller device becomes unusable.